Seatbelt restraint systems for restraining an occupant in a vehicle seat play an important role in reducing occupant injury in vehicle crash situations. Seatbelt restraint systems of the conventional so-called “3-point” variety commonly have a lap belt section extending across the seat occupant's pelvis and a shoulder belt section crossing the upper torso, which are fastened together or are formed by a continuous length of seatbelt webbing. The lap and shoulder belt sections are connected to the vehicle structure by anchorages. A belt retractor is typically provided to store belt webbing and may further act to manage belt tension loads in a crash situation.
Seatbelt restraint systems which are manually deployed by the occupant (so-called “active” types) also typically include a buckle attached to the vehicle body structure by an anchorage. A latch plate attached to the belt webbing is received by the buckle to allow the belt system to be fastened for enabling restraint, and unfastened to allow entrance and egress from the vehicle. Seatbelt systems, when deployed, effectively restrain the occupant during a collision.
One type of pretensioning device is a pyrotechnic lap pretensioner (PLP). PLPs are attached to a webbing guide loop or a seatbelt anchorage. Typical PLPs having included a pyrotechnic charge that is fired when a collision occurs, producing expanding gas which pressurizes a gas chamber within a tube, which forces a piston down the tube. The piston is connected with the belt system by a cable or strap. Stroking of the piston tightens or “pretensions” the belt against the occupant.
In order to provide enhanced occupant ingress and egress in two-door style vehicles, the lower anchorage end of the lap belt portion of the seat belt can be attached to a slider bar. The slider bar is mounted to the vehicle floor pan at the rear outboard corners of the front occupant seats. The slider bar allows the lower anchorage end of the seat belt webbing that is normally anchored solidly to the vehicle floor pan or sill plate to slide backwards to allow ingress and egress to and from the rear seat area of the vehicle. When the front seat occupant dons the seat belt, the lower anchorage end of the seat belt slides forward and is solidly anchored at the front end of the slider bar. One drawback to this type of hardware is that it cannot be easily used in conjunction with a pyrotechnic lap pretensioner (PLP) being used today in the automotive industry.
Another design constraint in the design of PLP's is attributed to the fact that normally a piston sliding within the gas cylinder of the PLP includes a cable (or rod) which is pulled through the cylinder when the pyrotechnic charge is ignited. As the piston is moved along the tube, it pulls the cable through the gas cylinder of the PLP. A seal is required where the cable passes out of the gas cylinder where it is anchored to a belt system component. The presence of the cable in the gas cylinder results in a gas leakage path created where the cable passes through the gas chamber. This increases the complexity of the PLP and increases the gas production capacity required for the gas generator. It is a desirable design feature to eliminate the cable or other mechanism present within the gas cylinder of the PLP to thereby provide a completely sealed gas chamber.